[FLASH-USERS] Expansion of Target

[Brian Kraus]

Hi Klaus,

Thank you for this useful workaround, it certainly helps me understand
better how FLASH can be used.

Incidentally, I did try "freezing" the solid by lowering its temperature as
far as seemed reasonable (down to < 1 mK). Even here, artificial shocks
immediately evolved. (I did no careful study of how the shock
magnitude/propagation was affected.)

Thank you,
Brian
--
Brian Kraus
Princeton Plasma Physics Laboratory
Office: (609) 243-3205, Cell: (719) 306-5524
E-mail: bkraus at pppl.gov


On Fri, Apr 26, 2019 at 12:14 PM Klaus Weide <klaus at flash.uchicago.edu>
wrote:

> On Thu, 25 Apr 2019, Brian Kraus wrote:
>
> >                   I am not sure if these shocks affect any dynamics
> > from the laser, but it would be nice to properly model a solid that does
> > not support these relaxation shocks.
>
> FLASH currently does not track interfaces between materials explicitly,
> and does not know about things such as surface tension or the properties
> of solids such as pressure and tensile forces.  So an initial condition
> with a strong pressure gradient somewhere - especially a jump such as
> at a solid-gas boundary - will unavoidably lead to some motion.
>
> A workaround that I have used is to "freeze" the solid material until it
> is significantly heated. I don't mean by lowering the initial temperature
> (although that might help, too), but by initially making the interface of
> the solid material act like a domain boundary as far as hydrodynamics is
> concerned. This can be done by using BDRY_VAR and setting it to +1 in the
> solid. After heating (such as by a laser) has started, cells whose
> temperature exceeds some threshold can be released by setting the BDRY_VAR
> value to -1. This can be done every time step in
> Simulation_adjustEvolution, for example.
>
> Klaus
>
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